Big Media describe DRM as Digital Rights Management. However, since its purpose is to restrict you the user, it is more accurate to describe DRM as Digital Restrictions Management. DRM Technology can restricts users’ access to movies, music, literature and software, indeed all forms of digital data.
The previous post was correct about needing to convert itunes M4a files to MP3. Unless your unit is an apple...it probably wont read or play M4a files.